Rubber-modified resin and thermoplastic resin composition containing the same

ABSTRACT

A rubber-modified resin obtained by conducting polymerization of a vinyl monomer in the presence of a mixed rubber latex of a silicone rubber latex (A) and an acrylic rubber latex (B), during which polymer particles are coagglomerated to enhance the particle size. The rubber-modified resin is useful as impact modifier and provides thermoplastic resin compositions having an excellent impact resistance by the incorporation thereof into thermoplastic resins.

TECHNICAL FIELD

[0001] The present invention relates to a rubber-modified resin usefulas an impact modifier for thermoplastic resins, and a thermoplasticresin composition containing the same. More particularly, the presentinvention relates to a rubber-modified resin wherein a resin is modifiedwith two rubbers of a silicone rubber and an acrylic rubber, and athermoplastic resin composition having an excellent impact resistance.

BACKGROUND ART

[0002] It has been popularly practiced to improve the impact resistanceof thermoplastic resins by incorporating a rubber-modified resincontaining a rubber component into the thermoplastic resins.

[0003] It has been considered advantageous in exhibiting impactresistance to use a rubber component having a glass transitiontemperature (Tg) as low as possible. In practice, a resin compositionincorporated with a resin modified with a polybutadiene-based rubberhaving a low Tg of about −80° C., e.g., acrylonitrile/butadiene/styrenecopolymer (ABS resin), has a higher impact resistance than a resincomposition incorporated with a resin modified with a polybutyl acrylaterubber having a Tg of about −50° C.

[0004] In respect of low Tg of rubbers, a polyorganosiloxane rubber(hereinafter also referred to as “silicone rubber”) can be expected toimpart a higher impact resistance as compared with rubber-modifiedresins containing a polybutadiene-based rubber component ifrubber-modified resins containing a silicone rubber can be utilized asimpact modifier, since for example the Tg of polydimethylsiloxane rubberis about −120° C.

[0005] Use of silicone rubber is also advantageous from the viewpoint ofweatherability as being superior to polybutyl acryalate rubber andpolybutadiene-based rubber.

[0006] From such a point of view, recently, it has been variouslyinvestigated to use resins modified with silicone rubber or compositerubbers containing silicone rubber as an impact modifier forthermoplastic resins. For example, JP-A-4-100812 discloses using a graftcopolymer prepared by graft-polymerizing a vinyl monomer onto acomposite rubber wherein a silicone rubber component and a polyalkyl(meth)acrylate component are unseparably entangled with each other.Also, JP-A-11-100481 discloses using a graft copolymer prepared byco-agglomerating silicone rubber particles and acrylic rubber particlesto give a composite rubber of enhanced particle size andgraft-polymerizing a vinyl monomer onto the composite rubber.

[0007] The impact resistance of thermoplastic resins is further improvedby incorporation of, as an impact modifier, these graft copolymersprepared using the composite rubbers as mentioned above in compared withsingle use of conventional rubbers such as polybutadiene-based rubberand acrylic rubber. However, the degree of improvement is not so largeas one expects.

[0008] It is an object of the present invention to provide an impactmodifier having a remarkably improved effect of imparting impactresistance.

[0009] A further object of the present invention is to provide athermoplastic resin composition having an improved impact resistance.

DISCLOSURE OF INVENTION

[0010] The present inventors have found that a rubber-modified resinhaving a remarkably improved impact resistance-imparting effect can beprepared by polymerizing a vinyl monomer in the presence of a mixedrubber latex of a silicone rubber latex and an acrylic rubber latex and,during the polymerization, coagglomerating polymer particles present inthe mixed latex to enhance the particle size.

[0011] Thus, the present invention provides a rubber-modified resinobtained by polymerizing a vinyl monomer in the presence of (A) asilicone rubber latex and (B) an acrylic rubber latex and, during thepolymerization, coagglomerating polymer particles to enhance theparticle size.

[0012] The rubber-modified resin of the present invention contains asilicone rubber and an acrylic rubber as the rubber component. Thesilicone rubber used in the present invention comprehends apolyorganosiloxane and a modified polyorganosiloxane wherein apolyorganosiloxane is partly replaced with an organic polymer having nopolyorganosiloxane segment. It is preferable that the amount of silicone(polyorganosiloxane) in the total rubber component of themodified-rubber resin is from 1 to 90% by weight based on 100% by weightof the total of the silicone rubber and the acrylic rubber. Also, it ispreferable that the amount of the total rubber latex is from 40 to 98parts by weight (solid basis) and the amount of the vinyl monomer isfrom 2 to 60 parts by weight, respectively, based on 100 parts by weightof the total of the whole rubber component and the vinyl monomer.Preferably the particle size enhancement by coagglomeration is conductedby adding an electrolyte to the polymerization system on or before thepolymerization conversion of the vinyl monomer reaches 90% by weight,especially when the polymerization conversion reaches 10 to 70% byweight.

[0013] The rubber-modified resin of the present invention can beincorporated into various thermoplastic resins, whereby the impactresistance of the thermoplastic resins is remarkably improved.

[0014] Thus, the present invention also provides a thermoplastic resincomposition comprising a thermoplastic resin and 0.1 to 150 parts byweight of the above-mentioned rubber-modified resin per 100 parts byweight of the thermoplastic resin.

BEST MODE FOR CARRYING OUT THE INVENTION

[0015] The rubber-modified resins of the present invention are thoseprepared by polymerizing a vinyl monomer in the presence of a mixedrubber latex of (A) a silicone rubber latex and (B) an acrylic rubberlatex and, during the polymerization, coagglomerating polymer particlesin the latex to enhance the particle size. That is to say, therubber-modified resins comprise particles formed by particlesize-enhancing co-agglomeration, which is conducted in the course of thegraft polymerization, of graft copolymer particles wherein a vinylmonomer is graft-polymerized onto a silicone rubber (or particleswherein the silicone rubber and a polymer of the vinyl monomer arephysically coexist if the silicone rubber has no grafting site) andgraft copolymer particles wherein the vinyl monomer is graft-polymerizedonto an acrylic rubber (or particles wherein the acrylic rubber and thevinyl polymer are physically coexist if the acrylic rubber has nografting site).

[0016] The rubber-modified resins of the present invention have theadvantage of being superior in impact resistance-imparting effect ascompared with a rubber-modified resin prepared in the same manner as thepresent invention but without conducting the particle size enhancingcoagglomeration during the polymerization of vinyl monomer, and arubber-modified resin prepared in such a manner as coagglomerating alatex of a mixed rubber (silicone rubber and acrylic rubber) prior tothe polymerization of vinyl monomer, namely a graft copolymer preparedby graft-polymerizing a vinyl monomer onto a composite rubber ofsilicone rubber and acrylic rubber.

[0017] The term “silicone rubber” as used herein comprehends apolyorganosiloxane having rubber elasticity, namely a conventionalsilicone rubber, a modified silicone rubber composed of a siliconerubber and an organic polymer having no silicone (polyorganosiloxane)segment (e.g., butyl acrylate polymer rubber, butadiene polymer rubber,styrene polymer, styrene-butyl acrylate copolymer, styrene-acrylonitrilecopolymer or methyl methacrylate polymer), and the like. The modifiedsilicone rubber includes a modified silicone rubber wherein a siliconerubber and an organic polymer having no silicone segment are chemicallybonded, a modified silicone rubber wherein a silicone rubber and anorganic polymer having no silicone segment are entangled, and a modifiedsilicone rubber wherein a silicone rubber and an organic polymer havingno silicone segment merely coexist without entangling each other.

[0018] The term “acrylic rubber” as used herein means a rubber(elastomer) containing at least 50% by weight, especially at least 60%by weight, of units of a (meth)acrylic monomer.

[0019] From the viewpoint of easiness in particle size enhancement bycoagglomeration operation mentioned after, it is preferable that thesilicone rubber particles included in the silicone rubber latex (A) havean average particle size of 10 to 200 nm, especially 20 to 150 nm.

[0020] The content of solvent-insoluble matter in the silicone rubberparticles, namely the gel content of the silicone rubber, denotes aweight percentage of a toluene-insoluble matter measured by immersing asample in toluene at room temperature for 24 hours and centrifuging at12,000 rpm for 1 hour. It is also preferable from the viewpoint ofexhibiting impact strength that the content of solvent-insoluble matterin the silicone rubber particles is from 0 to 100% by weight, especially40 to 100% by weight.

[0021] The content of silicone (polyorganosiloxane) component includedin the silicone rubber particles is not particularly limited, but ispreferably at least 50% by weight, especially at least 60% by weight,from the viewpoint of exhibiting impact resistance. The maximum valuethereof is 100% by weight.

[0022] Examples of the silicone rubber are, for instance,dimethylsiloxane rubber, a modified silicone rubber composed of butylacrylate rubber and dimethylsiloxane rubber which are chemically bonded,a modified silicone rubber composed of butyl acrylate rubber anddimethylsiloxane rubber which are entangled with each other, a modifiedsilicone rubber composed of butyl acrylate rubber and dimethylsiloxanerubber which merely coexist without being entangled with each other, amodified silicone rubber composed of styrene-butyl acrylate copolymerand dimethylsiloxane rubber which are chemically bonded, a modifiedsilicone rubber composed of styrene-butyl acrylate copolymer anddimethylsiloxane rubber which are entangled with each other, a modifiedsilicone rubber composed of styrene-butyl acrylate copolymer anddimethylsiloxane rubber which merely coexist without being entangledwith each other, and the like.

[0023] The silicone rubber latex (A) used in the present inventionusually has a solid concentration of 10 to 50% by weight (measured afterdrying at 120° C. for 1 hour). Silicone rubber latex (A) having a solidconcentration of 20 to 40% by weight is preferred from the viewpoint ofeasiness in controlling the particle size by the particle sizeenhancement operation mentioned after.

[0024] The silicone rubber latex (A) is prepared, for instance, byemulsion polymerization using, as a main component, a siliconerubber-forming component comprising an organosiloxane (a) and optionallya crosslinking agent (b), a graftlinking agent (c) and otherorganosilane (d) than those used as the crosslinking agent and thegraftlinking agent.

[0025] The organosiloxane (a) is a component which constitutes thebackbone of the silicone rubber chains, and linear and cyclicorganosiloxanes can be used. Cyclic organosiloxanes are preferred fromthe viewpoints of applicability to emulsion polymerization system andeconomy. Examples of the cyclic organosiloxane are, for instance,hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4),decamethylcyclopentasiloxane (D5), dedecamethylcyclohexasiloxane (D6),tetradecamethylcycloheptasiloxane (D7), hexadecamethylcyclooctasiloxane(D8), and the like. The organosiloxanes may be used alone or inadmixture thereof. In particular, D4, a mixture of D3 to D7 and amixture of D3 to D8 are preferably used from an economical point ofview.

[0026] The crosslinking agent (b) is optionally used for the purpose ofintroducing a crosslinked structure into the silicone rubber bycopolymerization with the organosiloxane (a), thereby imparting a rubberelasticity to the silicone rubber. Examples thereof are, for instance,tetrafunctional and trifunctional alkoxysilane compounds such astetramethoxysilane, tetraethoxysilane, triethoxymethylsilane,triethoxyethylsilane, butyltrimethoxysilane, butyltriethoxysilane,propyltrimethoxysilane and octyltrimethoxysilane, and othertetrafunctional and trifunctional silane compounds. These may be usedalone or in admixture thereof. Of these, alkoxysilane compounds having aC₂ to C₈ monovalent hydrocarbon group are preferred from the viewpointsof imparting an affinity with acrylic rubber component to the obtainedsilicone rubber to thereby controlling the impact resistance-impartingeffect.

[0027] The graftlinking agent (c) includes reactive silane compoundshaving a polymerizable unsaturated bond or a mercapto group in theirmolecules. It is optionally used for the purpose of introducingpolymerizable unsaturated bonds or mercapto group into the side chainsor molecular chain ends of copolymers by the copolymerization with theorganosiloxane and optionally the crosslinking agent and the like. Thepolymerizable unsaturated bond or mercapto group serves as an activesite for grafting of vinyl monomers mentioned after. The polymerizableunsaturated bond or mercapto group also serves as a crosslinking pointwhich forms crosslinkages by a radical reaction between them through aradical polymerization initiator. Even in the case that crosslinking isconducted by radical reaction, a part of the unsaturated bonds ormercapto groups remain as a grafting point and, therefore, grafting ispossible.

[0028] Examples of the reactive silane compound having a polymerizableunsaturated bond in its molecule are, for instance, a silane compound ofthe formula (1):

[0029] wherein R¹ is hydrogen atom or methyl group, R² is a monovalenthydrocarbon group having 1 to 6 carbon atoms, X is an alkoxyl grouphaving 1 to 6 carbon atoms, a is 0, 1 or 2, and p is an integer of 1 to6, a silane compound of the formula (2):

[0030] wherein R², X, a and p are as defined above, a silane compound ofthe formula (3):

[0031] wherein R², X and a are as defined above, a silane compound ofthe formula (4):

[0032] wherein R², X and a are as defined above, and R³ is a bivalenthydrocarbon group having 1 to 6 carbon atoms, and the like.

[0033] Examples of the group R² in the formulas (1) to (4) are, forinstance, an alkyl group such as methyl group, ethyl group or propylgroup, phenyl group, and the like. Examples of the group X are, forinstance, an alkoxyl group having 1 to 6 carbon atoms such as methoxygroup, ethoxy group, propoxy group or butoxy group, and the like.Examples of the group R³ in the formula (4) are, for instance, methylenegroup, ethylene group, trimethylene group, tetramethylene group, and thelike.

[0034] Examples of the reactive silane compound (1) are, for instance,β-methacryloyloxyethyldimethoxymethylsilane,γ-methacryloyloxy-propyldimethoxymethylsilane,γ-methacryloyloxypropyltrimethoxysilane,γ-methacryloyloxypropyldimethylmethoxysilane,γ-methacryloyloxypropyltriethoxysilane,γ-methacryloyloxypropyldiethoxymethylsilane,γ-methacryloyloxypropyltripropoxysilane,γ-methacryloyloxypropyldipropoxymethylsilane,γ-acryloyloxypropyldimethoxymethylsilaneγ-acryloyloxypropyltrimethoxysilane, and the like. Examples of thereactive silane compound (2) are, for instance,p-vinylphenyldimethoxymethylsilane, p-vinylphenyltrimethoxysilane,p-vinylphenyltriethoxysilane, p-vinylphenyldiethoxymethylsilane, and thelike. Examples of the reactive silane compound (3) are, for instance,vinylmethyldimethoxysilane, vinylmethyldiethoxysilane,vinyltrimethoxysilane, vinyltriethoxysilane, and the like. Examples ofthe reactive silane compound (4) are, for instance,allylmethyldimethoxysilane, allylmethyldiethoxysilane,allyltrimethoxysilane, allyltriethoxysilane, and the like. Of these,silane compounds of the formulas (1) and (3) are preferably used fromthe viewpoints of economy and reactivity.

[0035] A typical example of the reactive silane compound having mercaptogroup in its molecule is a silane compound of the formula (5):

[0036] wherein R², X and a are as defined above, and R⁴ is a bivalentorganic group such as an alkylene group having 1 to 18 carbon atoms.Examples of the alkylene group are, for instance, methylene group,ethylene group, trimethylene group, tetramethylene group and the like.

[0037] Examples of the reactive silane compound (5) are, for instance,mercaptopropyltrimethoxysilane, mercaptopropyldimethoxymethylsilane, andthe like.

[0038] Reactive silane compounds of trialkoxysilane type serve both as agraftlinking agent and as a crosslinking agent.

[0039] The organosilanes (d) other than the above-mentioned crosslinkingagent (b) and graftlinking agent (c) serve to impart an affinity with anacrylic rubber to the obtained silicone rubbers. They include, forinstance, organosilane compounds having a structural unit of the formula(6):

[0040] wherein R⁵ and R⁶ are a monovalent hydrocarbon group having 1 to10 carbon atoms, e.g., methyl group, ethyl group, propyl group or phenylgroup, and R⁵ and R⁶ may be the same or different unless they aresimultaneously methyl group. Examples of the organosilane having thestructural unit (6) are, for instance, methylbutyldimethoxysilane,dibutyldimethoxysilane, methyloctyldimethoxysilane,phenylmethyldimethoxysilane, diphenyldimethoxysilane and otherdialkoxysilane compounds. These may be used alone or in admixturethereof. If the organosiloxane (a), crosslinking agent (b) orgraftlinking agent (c) has the structural unit of the formula (6), thereis no need to use the other organosilane (d).

[0041] With respect to the proportions of the organosiloxane (a),crosslinking agent (b), graftlinking agent (c) and other organosilane(d) in the silicone rubber-forming component, it is preferable that theproportion of the organosiloxane (a) is from 59.9 to 99.9% by weight,especially 70 to 99% by weight, the proportion of the crosslinking agent(b) is from 0 to 40% by weight, especially 0.5 to 20% by weight, theproportion of the graftlinking agent (c) is from 0 to 40% by weight,especially 0.5 to 20% by weight, and the proportion of the otherorganosilane (d) is from 0 to 40% by weight, especially 0 to 29% byweight (the total of (a) to (d) is 100% by weight). The crosslinkingagent and the graftlinking agent are optional components, but it ispreferable that the amounts of the crosslinking agent and thegraftlinking agent are not simultaneously 0% by weight and either ofthem is used in an amount of at least 0.1% by weight. If the proportionof the organosiloxane is too small, the product lacks properties as arubber, so the impact resistance-imparting effect is decreased. If theproportion of organosiloxane is too large, the amounts of thecrosslinking agent, graftlinking agent and other organosilane become tosmall, so the effects produced by the use thereof tend to be exhibitwith difficulty. Also, if the proportion of the crosslinking agent orgraftlinking agent is too small, the impact resistance-imparting effectis small, and if the proportion is too large, the product lacksrubber-like properties, so the impact resistance-imparting effect alsotends to be lowered. The other organosilane (d) is an optionalcomponent. An affinity with acrylic rubber component is provided by theuse thereof, whereby the impact resistance-imparting effect can beadjusted. However, it is preferable to use the other organosilane (d)under consideration of balance between the cost and the physicalproperties, since the use thereof leads to increase in cost.

[0042] The silicone rubber latex (A) can be prepared, for example, by amethod wherein the silicone rubber-forming component comprising theorganosiloxane and optionally the crosslinking agent and thegraftlinking agent and further optionally the other organosilane isemulsified and dispersed into water by mechanical shearing in thepresence of an emulsifier and is polymerized under acidic condition. Incase of preparing modified silicone rubbers, the silicone rubber-formingcomponent is used in combination with a vinyl monomer component. In casethat emulsified droplets having a size of not less than severalmicrometers have been formed by mechanical shearing, it is possible tocontrol the average particle size of the silicone rubber particlesobtained after the polymerization within the range of 20 to 400 nmdepending on the amount of an emulsifier used. It is also possible toobtain the particles whose variation coefficient (100×standarddeviation/average particle size) (%) in the particle size distributionthereof is not more than 70%.

[0043] Also, when it is desired to prepare a silicone rubber having anaverage particle size of not more than 100 nm and a narrow particle sizedistribution, it is preferable to carry out the polymerization inmultistages. For example, 1 to 20% by weight of an emulsion comprisingemulsified droplets of not less than several micrometers obtained byemulsifying the silicone rubber-forming component, water and anemulsifier by means of mechanical shearing thereof is previouslysubjected to emulsion polymerization under an acidic condition, and theremaining emulsion is then added and polymerized in the presence of theproduced silicone rubber as seeds. In case of preparing the siliconerubber in such a manner, it is possible to control the average particlesize within the range of 20 to 100 nm depending on the amount of anemulsifier used, and also to control the variation coefficient in theparticle size distribution to not more than 60%. More preferable is amultistage polymerization method wherein a vinyl (co)polymer prepared byhomo- or copolymerizing a vinyl monomer, e.g., a vinyl monomer as usedin the graft polymerization mentioned after (such as styrene, butylacrylate or methyl acrylate) in a usual emulsion polymerization manneris used as seeds instead of the silicone rubber seeds in the abovemultistage polymerization, and a multistage polymerization is carriedout in the same manner as above. According to such a method, it ispossible to control the average particle size of the obtained siliconerubber (modified silicone rubber) within the range of 10 to 100 nm andthe variation coefficient in the particle size distribution to not morethan 50% depending on the amount of an emulsifier used.

[0044] The emulsion droplets of not less than several micrometers can beprepared by using a high speed agitating machine such as a homogenizer.

[0045] In these methods are used emulsifiers which do not lose anability as emulsifier even under an acidic condition. Examples of suchemulsifiers are, for instance, alkylbenzenesulfonic acid, sodiumalkylbenzenesulfonate, alkylsulfonic acid, sodium alkylsulfonate, sodium(di)alkyl sulfosuccinate, sodium polyoxyethylene nonylphenyl ethersulfonate, sodium alkylsulfate, and the like. These may be used alone orin admixture thereof.

[0046] Preferably the acidic condition is adjusted to a pH of 1 to 3 byadding an inorganic acid such as sulfuric acid or hydrochloric acid oran organic acid such as alkylbenzenesulfonic acid, alkylsulfonic acid ortrifluoroacetic acid to the polymerization system, since the rate ofpolymerization is adequate.

[0047] The polymerization temperature to form the silicone rubber ispreferably from 60 to 120° C., more preferably from 70 to 100° C., sincethe rate of polymerization is adequate.

[0048] The silicone rubber latex is obtained in such a manner, but underan acidic condition the Si—O—Si bonds which constitute the backbone ofsilicone rubber are in an equilibrium state between severance andformation, and this equilibrium varies depending on the temperature.Accordingly, for the purpose of stabilization of silicone rubber chains,it is preferable to neutralize the latex by addition of an aqueoussolution of an alkali such as sodium hydroxide, potassium hydroxide orsodium carbonate. The equilibrium shifts to the formation side as thetemperature lowers and, therefore, a silicone rubber having a highmolecular weight or a high degree of crosslinking is easy to beproduced. Thus, when it is desired to obtain a silicone rubber having ahigh molecular weight or a high degree of crosslinking, it is preferablethat after conducting the polymerization for the production of siliconerubbers at a temperature of 60° C. or higher, the reaction mixture iscooled to room temperature or in the vicinity thereof, maintained atthat temperature for about 5 to about 100 hours and then neutralized.

[0049] Acrylic rubber latex (B) used in the present invention is, asmentioned above, a latex of an acrylic rubber containing 50 to 100% byweight of units of a (meth)acrylic monomer. Any acrylic rubbers can beused without particular restriction so long as they have properties as arubber. Examples thereof are, for instance, a latex of poly(butylacrylate) rubber, a latex of poly(2-ethylhexyl acrylate) rubber, a latexof butyl acrylate-2-ethyl hexyl acrylate copolymer rubber, a latex of acomposite rubber of poly(butyl acrylate) and poly(2-ethylhexylacrylate), and the like.

[0050] The acrylic rubber latex (B) usually has a solid concentration of10 to 50% by weight (measured after drying at 120° C. for 1 hour).Acrylic rubber latex (B) having a solid concentration of 20 to 40% byweight is preferred from the viewpoint of easiness in controlling theparticle size by the particle size enhancement operation mentionedafter.

[0051] From the viewpoint of easiness in particle size enhancement bycoagglomeration operation mentioned after, it is preferable that therubber particles included in the acrylic rubber latex (B) have anaverage particle size of 10 to 200 nm, especially 20 to 150 nm.

[0052] From the viewpoint of exhibiting impact strength, it ispreferable that the content of solvent-insoluble matter in the rubberparticles of the acrylic rubber latex (B) (gel content: weight fractionof a toluene-insoluble matter measured by immersing a sample in tolueneat room temperature for 24 hours and centrifuging at 12,000 rpm for 1hour) is not less than 70% by weight, especially not less than 80% byweight. The maximum gel fraction is 100% by weight.

[0053] Examples of the acrylic rubber are, for instance, polybutylacrylate rubber, butyl acrylate-2-ethylhexyl (meth)acrylate copolymerrubber, a composite rubber of polybutyl acrylate and poly2-ethylhexyl(meth)acrylate, butyl acrylate-butadiene copolymer rubber, butylacrylate-styrene copolymer rubber, and the like. The acrylic rubbers maybe used alone or in admixture thereof. The term “copolymer” as usedherein comprehends random copolymers, block copolymers, graft copolymersand combinations thereof.

[0054] The acrylic rubber latex can be obtained by polymerizing amonomer mixture of an alkyl (meth)acrylate monomer, a polyfunctionalmonomer containing at least two polymerizable unsaturated bonds in itsmolecule, other copolymerizable monomers and the like in the presence ofa radical polymerization initiator and optionally a chain transfer agentaccording to a conventional emulsion polymerization method, for example,by methods as described in JP-A-50-88169 and JP-A-61-141746.

[0055] The alkyl (meth)acrylate monomer is a component which constitutesthe main backbone of the acrylic rubber. Examples thereof are, forinstance, an alkyl acrylate having a C₁ to C₁₂ alkyl group such asmethyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate or2-ethylhexyl acrylate, an alkyl methacrylate having a C₄ to C₁₂ alkylgroup such as 2-ethylhexyl methacrylate or lauryl methacrylate, and thelike. These may be used alone or in admixture thereof. Of these, amonomer mixture containing 40 to 100% by weight, especially 60 to 100%by weight, of butyl acrylate is preferred from the viewpoints of lowglass transition temperature of the obtained polymers and economy, inwhich the residual comonomer is for instance methyl acrylate, ethylacrylate, 2-ethylhexyl acrylate or the like.

[0056] The polyfunctional monomer containing at least two polymerizableunsaturated bonds in its molecule is a component used for introducing acrosslinked structure to the acrylic rubber particles to form a networkstructure, thereby exhibiting a rubber elasticity, and for providing anactive site for grafting of vinyl monomers mentioned after. Examples ofthe polyfunctional monomer are, for instance, dially phthalate, triallylcyanurate, trially isocyanurate, allyl methacrylate, ethyleneglycoldimethacrylate, divinyl benzene, other known allyl, di(meth)acrylate anddivinyl compounds, and the like. These may be used alone or in admixturethereof. Of these, allyl methacrylate, triallyl cyanurate, triallyisocyanurate and diallyl phthalatae are preferred from the viewpoints ofcrosslinking efficiency and grafting efficiency.

[0057] The other copolymerizable monomer may be optionally used for thepurpose of adjusting the refractive index of the obtained acrylicrubbers or the affinity with silicone rubbers. Examples thereof are, forinstance, methacrylic acid, a methacrylic ester monomer such as methylmethacrylate, ethyl methacrylate, glycidyl methacrylate, hydroxyethylmethacrylate or benzyl methacrylate, an aromatic vinyl monomer such asstyrene or α-methylstyrene, a vinyl cyanide monomer such asacrylonitrile or methacrylonitrile, a silicon-containing vinyl monomersuch as γ-methacryloyloxypropyldimethoxymethylsilane,γ-methacryloyloxypropyltrimethoxysilane or trimethylvinylsilane, and thelike. These may be used alone or in admixture thereof.

[0058] Preferable proportions of the monomers used in the production ofacrylic rubber latex are from 66.5 to 99.9% by weight, especially 85 to99.9% by weight, of the alkyl (meth)acrylate monomer, 0.1 to 10% byweight, especially 0.1 to 5% by weight of the polyfunctional monomercontaining two or more polymerizable unsaturated bonds in its molecule,and 0 to 23.4% by weight, especially 0 to 14.9% by weight, of the othercopolymerizable monomer, the total thereof being 100% by weight. If theproportion of the alkyl (meth)acrylate monomer is too small, theproducts lack properties as a rubber, so the impact resistance-impartingeffect is lowered. If the proportion of the alkyl (meth)acrylate is toolarge, the proportion of the polyfunctional monomer becomes too small,so the effects to be produced thereby tend to be insufficient. Also, ifthe proportion of the polyfunctional monomer is too small, thecrosslinking density is low, so the impact resistance-imparting effecttends to be lowered, and if the proportion is too large, thecrosslinking density becomes too high, so the impactresistance-imparting effect also tends to be lowered. The othercopolymerizable monomer is a component used for adjusting the refractiveindex or the impact resistance and, when it is desired to obtain theeffects to be produced by the use thereof, the amount thereof ispreferably not less than 0.1% by weight.

[0059] As the radical polymerization initiator used in the emulsionpolymerization for the preparation of the acrylic rubber latex and thechain transfer agent optionally used therein, those used in usualradical polymerization can be used without particular restriction.

[0060] Examples of the radical polymerization initiator are an organicperoxide such as cumene hydroperoxide, tert-butyl hydroperoxide, benzoylperoxide, tert-butylperoxy isopropylcarbonate, di-tert-butyl peroxide,tert-butylperoxy laurate, lauroyl peroxide, succinic acid peroxide,cyclohexanone peroxide or acetylacetone peroxide; an inorganic peroxidesuch as potassium persulfate or ammonium persulfate; an azo compoundsuch as 2,2′-azobisisobutylonitrile or2,2′-azobis-2,4-dimethylvaleronitrile; and the like. Of these, organicperoxides and inorganic peroxides are preferably used from the viewpointof a high reactivity.

[0061] In case of using organic peroxides or inorganic peroxides, theymay be used in combination with a reducing agent, e.g., a mixture offerrous sulfate/glucose/sodium pyrophosphate, a mixture of ferroussulfate/dextrose/sodium pyrophosphate, or a mixture of ferroussulfate/sodium formaldehyde sulfoxylate/ethylenediamineacetate. The useof a reducing agent is particularly preferable, since the polymerizationtemperature can be lowered.

[0062] The radical polymerization initiator is used usually in an amountof 0.005 to 10 parts by weight, preferably 0.01 to 5 parts by weight,more preferably 0.02 to 2 parts by weight, per 100 parts by weight of amonomer mixture used. If the amount of the initiator is too small, therate of polymerization is low, so the production efficiency tends to belowered, and if the amount is too large, the molecular weight of theobtained polymers is lowered, so the impact resistance tends to belowered.

[0063] Examples of the chain transfer agent are, for instance,t-dodecylmercaptan, n-octylmercaptane, n-tetradecylmercaptan,n-hexylmercaptan and the like.

[0064] The chain transfer agent is an optional component. From theviewpoint of exhibiting the impact resistance-imparting effect, it ispreferable that the amount thereof is from 0.001 to 5 parts by weightper 100 parts by weight of the monomer mixture.

[0065] Examples of the emulsifier used in emulsion polymerization forthe production of acrylic rubbers are, besides emulsifiers which can beused in the production of silicone rubber latex (A), fatty acid metalsalts such as potassium oleate, sodium oleate, potassium rhodinate,sodium rhodinate, potassium palmitate, sodium palmitate and potassiumstearate. These may be used alone or in admixture thereof.

[0066] The silicone rubber latex (A) and the acrylic rubber latex (B)are used preferably in such a ratio that the amount of silicone(polyorganosiloxane) is from 1 to 90% by weight, especially from 1 to50% by weight, more especially from 1 to 20% by weight, based on thewhole rubber component (silicone rubber plus acrylic rubber). An effectof imparting a high impact resistance to thermoplastic resins isobtained within this range. If the amount of the silicone included inthe whole rubber component is too small or too large, improvement inimpact resistance of thermoplastic resins tends to become insufficient.

[0067] In case that the amount of silicone is more than 50% by weight,it is preferable from the viewpoint of exhibiting impact resistance thatthe active sites for grafting are present in the silicone rubber, inother words, graft copolymers are produced by polymerization of vinylmonomers mentioned after. It is also preferable from the viewpoint ofimpact resistance that the acrylic rubber has active sites for graftingregardless of the amount of silicone.

[0068] From the viewpoint of easiness in particle size enhancement bycoagglomeration, it is preferable that the solid concentration of thewhole rubber latex (mixture of silicone rubber latex and acrylic rubberlatex) is from 10 to 50% by weight, especially from 20 to 40% by weight.

[0069] The rubber-modified resin of the present invention is obtained bypolymerizing a vinyl monomer in the presence of the mixed rubber latexand, during the polymerization, coagglomerating the polymer particles inthe latex to enhance the particle size.

[0070] The rubber-modified resin comprises, as mentioned above, resinparticles containing particles formed by particle size-enhancingco-agglomeration of graft copolymer particles wherein a vinyl monomer isgraft-polymerized onto silicone rubber particles of silicone rubberlatex (A) (or particles wherein the silicone rubber and a vinyl polymerare physically coexist if the silicone rubber particles have no graftingsite) and graft copolymer particles wherein the vinyl monomer isgraft-polymerized onto acrylic rubber particles (or particles whereinthe acrylic rubber and the vinyl polymer are physically coexist if theacrylic rubber particles have no grafting site). It is preferable thatthe average particle size of the resin particles is not less than 100nm, especially not less than 120 nm, and is not more than 1,000 nm,especially not more than 800 nm. If the average particle size is lessthan 100 nm or more than 1,000 nm, the impact resistance tends to lower.It is preferable that the content of a solvent-insoluble matter in therubber-modified resin is not less than 40% by weight, especially notless than 70% by weight, more especially not less than 80% by weight.

[0071] The “coagglomeration to enhance particle size” or “particle sizeenhancement by coagglomeration” denotes simultaneously agglomerating atleast two kinds of polymer particles having different chemicalcompositions in the same system to enhance the particle size.

[0072] The particle size-enhancing coagglomeration can be carried out bya conventional method using an electrolyte, for example, by adding,prior to the step of polymerizing a vinyl monomer or during this step,an inorganic salt such as sodium sulfate, an inorganic acid such ashydrochloric acid, an organic acid such as acetic acid, or a latex of anon-crosslinked acid group-containing copolymer obtained bycopolymerization of an unsaturated acid monomer and an alkyl(meth)acrylate monomer as disclosed in JP-A-50-25655, JP-A-8-12703 andJP-A-8-12704, to the polymerization system. When it is desired to obtaina rubber-modified resin having an average particle size of 100 to 400nm, it is preferable to use an inorganic salt, an inorganic acid or anorganic acid. An inorganic salt is particularly preferred since anoperation for adjusting the pH of the system after the completion of thecoagglomeration is omitted. When it is desired to obtain arubber-modified resin having an average particle size of 300 to 1,000nm, it is preferable to use the acid group-containing copolymer latex.

[0073] An example of the acid group-containing copolymer is, forinstance, copolymers of 5 to 25% by weight, especially 5 to 15% byweight, of at least one unsaturated acid such as acrylic acid,methacrylic acid, itaconic acid or crotonic acid, 45 to 95% by weight,especially 65 to 95% by weight, of at least one alkyl (meth)acrylatehaving a C₁ to C₁₂ alkyl group (preferably a mixture of 10 to 80% byweight of an alkyl acrylate having a C₁ to C₁₂ alkyl group and 20 to 90%by weight of an alkyl methacrylate having a C₁ to C₁₂ alkyl group), and0 to 30% by weight, especially 0 to 20% by weight, of at least one othervinyl monomer copolymerizable therewith.

[0074] In case of using an inorganic salt, an inorganic acid or anorganic acid as an electrolyte, preferably the amount thereof is from0.1 to 5 parts by weight, especially 0.2 to 4 parts by weight, moreespecially 0.3 to 3 parts by weight, per 100 parts by weight (solidbasis) of the mixed rubber latex. If the amount is too small, thecoagglomeration tends to be difficult. If the amount is too large, thereis a tendency that it is difficult to apply to industrial productionsince clots are easy to be produced.

[0075] In case of using an acid group-containing copolymer latex as anelectrolyte, preferably the amount thereof is from 0.1 to 10 parts byweight, especially 0.2 to 5 parts by weight, per 100 parts by weight(solid basis) of the mixed rubber latex. If the amount is too small, thecoagglomeration tends to occur with difficulty. If the amount is toolarge, unfavorable phenomenon such as lowering of impact resistance iseasy to occur.

[0076] The time of adding an electrolyte such as inorganic salt,inorganic acid, organic acid or acid group-containing copolymer latex tothe polymerization system to enhance the particle size is notparticularly limited so long as the coagglomeration takes place duringthe step of polymerizing a vinyl monomer in the presence of rubberparticles. From the viewpoint of impact resistance, it is preferable toadd the electrolyte to the polymerization system prior to starting thepolymerization or until 90% by weight of a vinyl monomer used for thepolymerization is polymerized (polymerization conversion 0 to 90% byweight), especially during the period after not less than 10% by weightof the vinyl monomer used for the polymerization is polymerized anduntil 70% by weight of the vinyl monomer used for the polymerization ispolymerized (polymerization conversion 10 to 70% by weight), moreespecially during the period after not less than 10% by weight of thevinyl monomer used for the polymerization is polymerized and until 50%by weight of the vinyl monomer used for the polymerization ispolymerized (polymerization conversion 10 to 50% by weight). Afteradding the electrolyte, the polymerization is further continued tocomplete the polymerization. Preferably, the polymerization is carriedout until the polymerization conversion of the vinyl monomer reaches atleast 95% by weight.

[0077] The polymerization temperature is from 30 to 90° C., preferablyfrom 40 to 80° C.

[0078] The vinyl monomer polymerized in the mixed rubber latex is acomponent for raising the affinity of a rubber-modified resin with athermoplastic resin to thereby uniformly disperse the rubber-modifiedresin into the thermoplastic resin in the case that the thermoplasticresin is incorporated with the rubber-modified resin and molded.

[0079] Examples of the vinyl monomer are, for instance, an aromaticvinyl monomer such as styrene, α-methylstyrene, p-methylstyrene ordivinyl benzene, a vinyl cyanide monomer such as acrylonitrile ormethacrylonitrile, a halogenated vinyl monomer such as vinyl chloride,vinylidene chloride or vinylidene fluoride, methacrylic acid, amethacrylic ester monomer such as methyl methacrylate, ethylmethacrylate, butyl methacrylate, glycidyl methacrylate, hydroxyethylmethacrylate, ethylene glycol dimethacrylate or 1,3-butylene glycoldimethacrylate, acrylic acid, an acrylic ester monomer such as methylacrylate, butyl acrylate, glycidyl acrylate or hydroxybutyl acrylate,and the like. The vinyl monomers may be used alone or in admixturethereof. Also, one or at least two vinyl monomers may be added andpolymerized in multistages. Of these, from the viewpoints of easiness inparticle size enhancement by coagglomeration and impact resistance ispreferred a monomer mixture containing 50 to 100% by weight, especially70 to 100% by weight, of a methacrylic ester monomer and/or an acrylicester monomer, the rest of which may be the above-mentioned aromaticvinyl monomer, vinyl cyanide monomer, halogenated vinyl monomer and thelike.

[0080] Preferably, the vinyl monomer is used in an amount of 2 to 60parts by weight, especially 5 to 40 parts by weight, more especially 8to 20 parts by weight, while the amount of the whole rubber latex (solidbasis) is from 40 to 98 parts by weight, especially 60 to 95 parts byweight, more especially 80 to 92 parts by weight, wherein the totalthereof is 100 parts by weight. If the amount of the vinyl monomer istoo large, there is a tendency that impact resistance is notsufficiently exhibited, since the content of rubber component becomestoo small. If the amount of the vinyl monomer is too small, the handlingtends to become difficult since the powdery state of the rubber-modifiedresin is deteriorated.

[0081] The polymerization of the vinyl monomer can be carried out by aconventional emulsion polymerization. As a radical polymerizationinitiator used therein and a chain transfer agent and an emulsifierwhich are optionally used therein, there may be used those usable in theproduction of the acrylic rubber latex. The limitations concerning theamounts of them in the production of the acrylic rubber latex are alsoapplicable to this case.

[0082] The rubber-modified resin obtained by the polymerization of thevinyl monomer may be isolated as a powder from the obtained latex or maybe used in the form of the latex. The isolation of the polymer may becarried out in a usual manner, for example, by adding a metal salt suchas calcium chloride, magnesium chloride or magnesium sulfate, or aninorganic or organic acid such as hydrochloric acid, sulfuric acid,phosphoric acid or acetic acid, to the latex to coagulate the latex,separating, washing with water, dehydrating and drying the polymer. Aspray-drying method is also applicable.

[0083] The thus obtained rubber-modified resin (in the state of powderor latex) is incorporated into various thermoplastic resins to givethermoplastic resin compositions having an improved impact resistance.

[0084] Examples of the thermoplastic resin are, for instance, polyvinylchloride, chlorinated polyvinyl chloride, polystyrene,styrene-acrylonitrile copolymer, styrene-acrylonitrile-N-phenylmaleimidecopolymer, α-methylstyrene-acrylonitrile copolymer, polymethylmethacrylate, methyl methacrylate-styrene copolymer, polycarbonate,polyamide, a polyester such as polyethylene terephthalate, polybutyleneterephthalate or 1,4-cyclohexanedimethanol-modified polyethyleneterephthalate, butadiene rubber-styrene copolymer (HIPS resin),acrylonitrile-butadiene rubber-styrene copolymer (ABS resin),acrylonitrile-acrylic rubber-styrene copolymer (AAS resin),acrylonitrile-ethylenepropylene rubber-styrene copolymer (AES resin),polyphenylene ether, and the like. These may be used alone or inadmixture thereof. Examples of a combination of at least two resins area mixed resin of 5 to 95% by weight of polycarbonate and 5 to 95% byweight of HIPS resin, ABS resin, AAS resin or AES resin (total thereof100% by weight), and a mixed resin of 5 to 95% by weight ofpolycarbonate and 5 to 95% by weight of polyethylene terephthalate orpolybutylene terephthalate (total thereof 100% by weight).

[0085] It is preferable, from the viewpoint of a balance of physicalproperties, that the amount of the rubber-modified resin is from 0.1 to150 parts by weight, especially from 0.5 to 120 parts by weight, per 100parts by weight of a thermoplastic resin. If the amount is too small,the impact resistance of thermoplastic resins is not sufficientlyimproved, and if the amount is too large, it is difficult to maintainthe properties such as rigidity and surface hardness of thethermoplastic resins.

[0086] Mixing of a thermoplastic resin with a solid powder of therubber-modified resin can be carried out by firstly mixing them througha Henschel mixer, a ribbon mixer or the like and then melt-kneading themixture through a roll mill, an extruder, a kneader or the like.

[0087] The thermoplastic resin compositions of the present invention maycontain usual additives, e.g., plasticizer, stabilizer, lubricant,ultraviolet absorber, antioxidant, flame retardant, pigment, glassfiber, filler, polymer processing aid, polymer lubricant andantidropping agent. For example, preferable examples of the flameretardant are a phosphorus compound such as triphenyl phosphate,condensed phosphate or stabilized red phosphorus, a silicone compoundsuch as phenyl group-containing polyorganosiloxane copolymer, and thelike. Preferable examples of the polymer processing aid are methacrylate(co)polymers such as methyl methacrylate-butyl acrylate copolymer.Preferable examples of the antidropping agent are fluorocarbon resinssuch as polytetrafluoroethylene. Preferable amounts of these additivesare, from the viewpoint of effect-cost balance, 0.1 to 30 parts byweight, especially 0.2 to 20 parts by weight, more especially 0.5 to 10parts by weight, per 100 parts by weight of a thermoplastic resin.

[0088] The thermoplastic resin composition can also be obtained bymixing a latex of a thermoplastic resin with a latex of therubber-modified resin and subjecting the mixed latex to coprecipitationof polymer particles.

[0089] Molding methods conventionally used for thermoplastic resincompositions, e.g., injection molding, extrusion, blow molding andcalendering, are applicable to the thermoplastic resin compositions ofthe present invention.

[0090] The obtained molded articles have excellent impact resistance ascompared with those using conventional impact modifiers.

[0091] The present invention is more specifically explained by means ofexamples, but it is to be understood that the present invention is notlimited to only these examples. In the following examples andcomparative examples, all parts and % excepting variation coefficientare by weight unless otherwise noted.

[0092] In the following examples and comparative examples, evaluationwas made in the following manners.

[0093] [Solid Concentration of Latex and Polymerization Conversion]

[0094] A sample of a latex obtained after reaction was dried in a hotair dryer at 120° C. for 1 hour to measure the solid concentration(heating residue). The polymerization conversion of a rubber latex wascalculated according to the equation: (amount of solid matter/amount ofmonomers charged)×100 (%).

[0095] [Average Particle Size]

[0096] Using as a measuring apparatus MICROTRAC UPA made by LEED &NORTHRUP INSTRUMENTS, the volume average particle size (nm) and thevariation coefficient in particle size distribution (standarddeviation/volume average particle size)×100 (%) were measured by a lightscattering method.

[0097] [Content of Solvent-insoluble Matter (Gel Fraction)]

[0098] A latex was dried firstly at 50° C. for 75 hours and then at roomtemperature for 8 hours under reduced pressure to give a test sample.The sample was immersed in toluene for 24 hours and centrifuged at12,000 r.p.m. for 60 minutes, and the weight percentage of thetoluene-insoluble matter in the sample was calculated.

[0099] [Izod Impact Strength]

[0100] The Izod impact strength was measured at −30° C., 0° C. and 23°C. by using a notched ¼ inch bar or a notched ⅛ inch bar according toASTM D-256.

[0101] [Flame Resistance]

[0102] Evaluation was made by UL94 V test.

Preparation Example 1

[0103] Preparation of Silicone Rubber Latex (A-1)

[0104] A five-necked flask equipped with a stirrer, a reflux condenser,an inlet for introducing nitrogen gas, an inlet for introducing monomersand a thermometer was charged with the following ingredients.Ingredients Amount (part) Pure water 189 Sodium dodecylbenzenesulfonate(SDBS) 0.5

[0105] The temperature was then raised to 70° C. with purging the systemwith nitrogen gas. Subsequently, after adding 1 part of pure water and0.02 part of potassium persulfate to the system, a mixed liquid of thefollowing ingredients was added at a time to the system, and was stirredfor 1 hour to complete the polymerization, thus giving a latex of ST-BMAcopolymer. Ingredients Amount (part) Styrene (ST) 0.7 Butyl methacrylate(BMA) 1.3

[0106] The polymerization conversion was 99%. The obtained latex had asolid content of 1.0%, an average particle size of 10 nm and a variationcoefficient of 38%. Also, the content of solvent-insoluble matter in theST-BMA copolymer was 0%.

[0107] Separately, an emulsion of a silicone rubber-forming componentwas prepared by stirring a mixture of the following ingredients at10,000 r.p.m. for 5 minutes with a homogenizer. Ingredients Amount(part) Pure water 70 SDBS 0.5 Octamethylcyclotetrasiloxane 94Vinyltriethoxysilane (VTES) 2 Tetraethoxysilane (TEOS) 2

[0108] Subsequently, the latex containing ST-BMA copolymer was kept at80° C., and thereto were added 2 parts of dodecylbenzene sulfonic acidand 18 parts of pure water to adjust the system to pH 1.7. The aboveemulsion of silicone rubber-forming component was added at a time to thelatex. The resulting mixture was stirred for 6 hours, and after coolingto 25° C. and allowing to stand for 20 hours, the mixture was adjustedto pH 8.4 with sodium hydroxide to finish the polymerization, thusgiving a silicone rubber latex (A-1). The polymerization conversion ofthe silicone rubber-forming component was 85%. The obtained latex (A-1)had a solid concentration of 23%, an average particle size of 90 nm anda variation coefficient in particle size distribution of 39%. Also, thecontent of solvent-insoluble matter was 71%. The silicone rubber in thesilicone rubber latex was composed of 98% of silicone component and 2%of ST-BMA copolymer component, which were calculated based on the chargeand conversion.

Preparation Example 2

[0109] Preparation of Silicone Rubber Latex (A-2)

[0110] Silicone rubber latex (A-2) was prepared in the same manner as inPreparation Example 1 except that vinyltriethoxysilane (VTES) wasreplaced with tetraethoxysilane (TEOS) so that the total amount of TEOSwas 3 parts. The obtained latex (A-2) had a solid concentration of 23%,an average particle size of 85 nm and a variation coefficient inparticle size distribution of 37%. Also, the content of solventinsoluble matter was 81%. The silicone rubber in the silicone rubberlatex was composed of 98% of silicone component and 2% of ST-BMAcopolymer component, which were calculated based on the charge andconversion.

Preparation Example 3

[0111] Preparation of Acrylic Rubber Latex (B-1)

[0112] A five-necked flask equipped with a stirrer, a reflux condenser,an inlet for introducing nitrogen gas, an inlet for introducing monomersand a thermometer was charged with the following ingredients at a time.Ingredients Amount (part) Pure water 200 Sodium oleate 1.3

[0113] The temperature was then raised to 70° C. with stirring in anitrogen stream. After reaching 70° C., a mixture of the followingingredients was added at a time to the system, and 0.05 part ofpotassium persulfate was further added. The resulting mixture wasstirred at 70° C. for 1 hour. Ingredients Amount (part) Butyl acrylate(BA) 4 Allyl methacrylate (AlMA) 0.04

[0114] Subsequently the following mixture was added dropwise over 5hours, and after the completion of the addition, the mixture was furtherstirred for 1 hour to complete the polymerization. Ingredients Amount(part) BA 96 AlMA 0.96

[0115] The polymerization conversion was 99%. The obtained latex had asolid concentration of 33%, an average particle size of 80 nm and avariation coefficient of 28%. Also, the content of solvent-insolublematter was 96%.

EXAMPLE 1

[0116] A five-necked flask equipped with a stirrer, a reflux condenser,an inlet for introducing nitrogen gas, an inlet for introducing monomersand a thermometer was charged with the following ingredients at a time.Ingredients Amount (part) Pure water 240 Silicone rubber latex (A-1)(solid basis) 11.9 Acrylic rubber latex (B-1) (solid basis) 73.1

[0117] The temperature was then raised to 70° C. with stirring in anitrogen stream and, after reaching 70° C., 0.03 part of potassiumpersulfate was added. Subsequently, 15 parts of methyl methacrylate(MMA) was added dropwise over 1 hour, during which 1.2 parts of sodiumsulfate was added to enhance the particle size by agglomeration when 3parts of MMA had been added. After the completion of the addition,stirring was further continued to complete the polymerization, thusgiving a latex of rubber-modified resin (I). The polymerizationconversion was 99%. The obtained rubber-modified resin particles had anaverage particle size of 185 nm and a solvent-insoluble matter contentof 90%.

[0118] The obtained latex was diluted with pure water to 15% in solidconcentration, and thereto was added 2 parts of calcium chloride tocoagulate the latex. The resulting slurry was once heated to 80° C., andwas then cooled, dehydrated and dried to give a powder of rubbermodified resin (I).

[0119] Into 100 parts of a vinyl chloride resin having a degree ofpolymerization of 800 were incorporated 7.0 parts of the rubber-modifiedresin (I), 3.0 parts of octyl tin mercaptide, 1.0 part of stearylalcohol, 0.5 part of stearic acid amide, 0.5 part of montanic acid diolester, 0.5 part of titanium oxide and 1.0 part of a high molecularprocessing aid commercially available under the trade mark of KANE ACEPA20 made by Kaneka Corporation. The mixture was melt-kneaded by a 50 mmsingle screw extruder (model VS50-26 made by Tanabe Plastic KikaiKabushiki Kaisha) to give pellets. The obtained pellets were molded byan injection molding machine (model IS-170G made by Toshiba Machine Co.,Ltd.) at a cylinder temperature of 195° C. to give ¼ inch Izod impacttest specimens. The results of the Izod impact test are shown in Table1.

EXAMPLE 2

[0120] A powder of rubber-modified resin (II) was prepared in the samemanner as in Example 1 except that the silicone rubber latex (A-2) wasused instead of the silicone rubber latex (A-1). The polymerizationconversion was 99%. The obtained rubber-modified resin particles had anaverage particle size of 180 nm and a solvent-insoluble matter contentof 89%.

[0121] The Izod impact test was made in the same manner as in Example 1except that the rubber-modified resin (II) was used instead of therubber-modified resin (I). The results are shown in Table 1.

EXAMPLE 3

[0122] A powder of rubber-modified resin (III) was prepared in the samemanner as in Example 1 except that a monomer mixture of 75% of ST and25% of acrylonitrile was used instead of MMA. The polymerizationconversion was 96%. The obtained rubber-modified resin particles had anaverage particle size of 160 nm and a solvent-insoluble matter contentof 88%.

[0123] The Izod impact test was made in the same manner as in Example 1except that the rubber-modified resin (III) was used instead of therubber-modified resin (I). The results are shown in Table 1.

Comparative Example 1

[0124] Polymerization of a vinyl monomer in the presence of rubberparticles was carried out without coagglomerating the rubber particlesto enhance the particle size.

[0125] That is to say, a powder of rubber-modified resin (I′) wasprepared in the same manner as in Example 1 except that sodium sulfatewas not added. The polymerization conversion was 99%. The obtainedrubber-modified resin particles had an average particle size of 85 nmand a solvent-insoluble matter content of 89%.

[0126] The Izod impact test was made in the same manner as in Example 1except that the rubber-modified resin (I′) was used instead of therubber-modified resin (I). The results are shown in Table 1.

Comparative Example 2

[0127] Polymerization of a vinyl monomer in the presence of rubberparticles was carried out in the same manner as in Example 1 except thata composite rubber previously obtained by particle size enhancingcoagglomeration was used instead of adding an electrolyte during thepolymerization.

[0128] That is to say, a flask was charged with 240 parts of pure water,11.9 parts (solid basis) of silicone rubber latex (A-1) and 73.1 parts(solid basis) of acrylic rubber latex (B-1) to give a mixed rubberlatex. To the mixed rubber latex were added 0.7 part of acetic acid andthen 0.5 part of NaOH at 70° C. in a nitrogen stream to give acoagglomerated rubber of enhanced particle size (composite rubber). Theaverage particle size of the composite rubber was 175 nm.

[0129] To the obtained composite rubber latex was added dropwise 15parts of MMA over 1 hour. After the completion of the addition, thereaction mixture was further stirred for 1 hour to complete thepolymerization, thus giving graft copolymer (II′) particles. Thepolymerization conversion was 99%. The obtained graft copolymerparticles had an average particle size of 185 nm and a solvent-insolublematter content of 90%.

[0130] The Izod impact test was made in the same manner as in Example 1except that the graft copolymer (II′) was used instead of therubber-modified resin (I). The results are shown in Table 1. TABLE 1Com. Com. Ex.1 Ex.2 Ex.3 Ex.1 Ex.2 Izod impact 23° C. 65 55 35 13 20strength (kJ/m²) 0° C. 11 10 9 7 8

[0131] From the results shown in Table 1, it would be understood that ahigh effect of improving impact resistance is exhibited by the use ofthe rubber-modified resin of the present invention as an impact modifierfor vinyl chloride resins.

EXAMPLE 4

[0132] Into 100 parts of a polycarbonate resin comprising2,2-bis(4-hydroxyphenyl)propane as a bisphenol component and having aweight average molecular weight of 23,000 were incorporated 3 parts ofthe rubber-modified resin (I) obtained in Example 1, 0.3 part of aphenolic stabilizer (TOPANOL CA made by ZENECA) and 0.3 part of aphosphorus stabilizer (ADEKASTAB PEP36 made by Asahi Denka Kogyo K. K).The mixture was melt-kneaded by a 40 mm single screw extruder (modelHW-40-28 made by Tabata Kikai Kabushiki Kaisha) to give pellets. Theobtained pellets were dried at 110° C. for more than 5 hours and moldedby an injection molding machine (model FAS100B made by Kabushiki KaishaFANUC) at a cylinder temperature of 290° C. to give ¼ inch Izod impacttest specimens. The specimens were subjected to the Izod impact test.The results are shown in Table 2.

Comparative Example 3

[0133] The Izod impact test was made in the same manner as in Example 4except that the graft copolymer (II′) obtained in Comparative Example 2was used instead of the rubber-modified resin (I). The results are shownin Table 2. TABLE 2 Example 4 Com. Ex. 3 Izod impact strength 68 59(kJ/m2) at 23° C.

[0134] From the results shown in Table 2, it would be understood that incase of using the rubber-modified resin of the present invention as animpact modifier for polycarbonate resins, it exhibits a higher effect ofimproving impact resistance as compared with a graft copolymercontaining a composite rubber composed of a silicone rubber and anacrylic rubber.

EXAMPLES 5 AND 6

[0135] A latex of rubber-modified resin (IV) was prepared in the samemanner as in Example 1 except that in the preparation of rubber-modifiedresin (I) of Example 1, there were changed the amount of silicone rubberlatex (A-1) to 18 parts (solid basis), the amount of acrylic rubberlatex (B-1) to 72 parts (solid basis), the amount of MMA to 10 parts andthe amount of sodium sulfate to 1.5 parts. The polymerization conversionof MMA was 99%. The obtained rubber-modified resin particles had anaverage particle size of 190 nm and a solvent-insoluble matter contentof 86%. The obtained latex was subjected to a coagulation treatment inthe same manner as in Example 1 to give a powder of rubber-modifiedresin (IV).

[0136] A composition was prepared using the obtained rubber-modifiedresin (IV) according to the recipe shown in Table 3, and wasmelt-kneaded by a twin screw extruder (model TEX44S made by The JapanSteel Works, Ltd.) to give pellets. The obtained pellets were dried at110° C. for more than 5 hours and molded by an injection molding machine(model FAS100B made by Kabushiki Kaisha FANUC) at a cylinder temperatureof 280° C. to give ⅛ inch test specimens for Izod impact test and{fraction (1/16)} inch test specimens for flame resistance evaluation.Using these specimens, the Izod impact test and flame resistanceevaluation were made. The results are shown in Table 3.

Comparative Examples 4 and 5

[0137] In Comparative Example 4, the procedure of Example 5 was repeatedexcept that the rubber-modified resin (I) was replaced with a siliconeflame retardant (KR-219 made by Shin-Etsu Chemical Co., Ltd.) and theflame retardant KR-219 was used in an amount of 8 parts.

[0138] In Comparative Example 5, the procedure of Example 5 was repeatedexcept that the rubber-modified resin (I) was not used without thereplacement thereof with the silicone flame retardant.

[0139] The results of the Izod impact test and flame resistanceevaluation are shown in Table 3.

Comparative Examples 6 and 7

[0140] In Comparative Example 6, the procedure of Example 6 was repeatedexcept that the rubber-modified resin (I) was not used.

[0141] In Comparative Example 7, the procedure of Example 6 was repeatedexcept that the rubber-modified resin (I) and the phosphorus-based flameretardant triphenyl phosphate were not used.

[0142] The results of the Izod impact test and flame resistanceevaluation are shown in Table 3. TABLE 3 Com. Com. Com. Com. Ex.5 Ex.6Ex.4 Ex.5 Ex.6 Ex.7 Thermoplastic resin PC 90 70 90 90 70 70 PET 10 3010 10 30 30 Impact modifier 2 3.5 0 0 0 0 Rubber-modified resin (IV)Flame retardant KR-219 6 0 8 0 0 0 Triphenyl 0 5 0 0 5 0 phosphateAntidropping 0.5 0.3 0.5 0.5 0.3 0.3 agent PTFE Stabilizer AO-60 0.1 0.20.1 0.1 0.2 0.2 PEP-36 0.1 0.3 0.1 0.1 0.3 0.3 Izod impact strength 8035 8 35 9 10 at 23° C. (kJ/m²) UL94 V V-1 V-0 V-1 below V-0 belowstandard standard

[0143] The ingredients shown in Table 3 are as follows:

[0144] PC: Polycarbonate resin comprising2,2-bis(4-hydroxyphenyl)propane as a bisphenol component and having aweight average molecular weight of 23,000

[0145] PET: Polyethylene terephthalate resin having a logarithmicviscosity of 0.75

[0146] KR-219: Silicone flame retardant KR-219 made by Shin-EtsuChemical Co., Ltd.

[0147] PTFE: Polytetrafluoroethylene

[0148] AO-60: Phenolic stabilizer (ADEKASTAB AO-60 made by Asahi DenkaKogyo K. K)

[0149] PEP36: Phosphorus stabilizer (ADEKASTAB PEP36 made by Asahi DenkaKogyo K. K)

[0150] From the results shown in Table 3, it is found that therubber-modified resin of the present invention can improve the impactresistance of a polycarbonate/polyethylne terephthalate blend flameretarded by a silicone flame retardant or a phosphorus flame retardantwhile maintaining the flame resistance of the blend.

EXAMPLE 7

[0151] Into 70 parts of a polycarbonate resin (LEXANE 121 made by GEPlastics Japan Ltd.) and 30 parts of an ABS resin (SUNTAC AT05 made byMitsui Chemicals, Inc.) were incorporated 5 parts of the rubber-modifiedresin (I) obtained in Example 1, 0.3 part of a phenolic stabilizer(TOPANOL CA made by ZENECA) and 0.3 part of a phosphorus stabilizer(ADEKASTAB PEP36 made by Asahi Denka Kogyo K. K). The mixture wasmelt-kneaded by a 40 mm single screw extruder (model HW-40-28 made byTabata Kikai Kabushiki Kaisha) to give pellets. The obtained pelletswere dried at 110° C. for more than 5 hours and molded by an injectionmolding machine (model FAS100B made by Kabushiki Kaisha FANUC) at acylinder temperature of 260° C. to give ¼ inch Izod impact testspecimens. The specimens were subjected to the Izod impact test. Theresults are shown in Table 4.

Comparative Example 8

[0152] The procedure of Example 7 was repeated except that therubber-modified resin (I) was not used. The results of Izod impact testare shown in Table 4. TABLE 4 Example 7 Com. Ex. 8 Izod impact 23° C. 4945 strength (kJ/m²) −30° C. 16 10

[0153] From the results shown in Table 4, it is found that therubber-modified resin of the present invention also exhibits an effectof improving impact resistance on a polycarbonate/ABS resin blend.

INDUSTRIAL APPLICABILITY

[0154] According to the present invention, rubber-modified resins havinga remarkably improved impact resistance-imparting effect can be obtainedby conducting polymerization of vinyl monomers in the presence of asilicone rubber latex and an acrylic rubber latex, during which polymerparticles are coagglomerated to enhance the particle size. Therubber-modified resins are applicable to various thermoplastic resins asimpact modifier, and thermoplastic resin compositions comprising therubber-modified resin and a thermoplastic resin have excellent impactresistance.

1. A rubber-modified resin obtained by polymerizing a vinyl monomer inthe presence of (A) a silicone rubber latex and (B) an acrylic rubberlatex and, during the polymerization, coagglomerating polymer particlesto enhance the particle size.
 2. The rubber-modified resin of claim 1,wherein the amount of silicone is from 1 to 90% by weight based on 100%by weight of the whole rubber component.
 3. The rubber-modified resin ofclaim 1 or 2, wherein 2 to 60 parts by weight of the vinyl monomer ispolymerized in the presence of 40 to 98 parts by weight (solid basis) ofthe whole rubber latex, the total thereof being 100 parts by weight. 4.The rubber-modified resin of any one of claims 1 to 3, wherein saidvinyl monomer is at least one member selected from the group consistingof aromatic vinyl monomers, vinyl cyanide monomers, halogenated vinylmonomers, (meth)acrylic acid and (meth)acrylic esters.
 5. Athermoplastic resin composition comprising 100 parts by weight of athermoplastic resin and 0.1 to 150 parts by weight of therubber-modified resin of claim
 1. 6. The composition of claim 5, whereinthe vinyl monomer used in the preparation of said rubber-modified resinis at least one member selected from the group consisting of aromaticvinyl monomers, vinyl cyanide monomers, halogenated vinyl monomers,(meth)acrylic acid and (meth)acrylic esters.
 7. The composition of claim5 or 6, wherein said thermoplastic resin is at least one member selectedfrom the group consisting of polyvinyl chloride, chlorinated polyvinylchloride, polystyrene, styrene-acrylonitrile copolymer,styrene-acrylonitrile-N-phenylmaleimide copolymer,α-methylstyrene-acrylonitrile copolymer, polymethyl methacrylate, methylmethacrylate-styrene copolymer, polycarbonate, polyamide, polyester,HIPS resin, ABS resin, AAS resin, AES resin and polyphenylene ether.